The present invention relates to parabolic antennas, such as are employed to receive and/or transmit carrier signals, and a method of forming such antennas and other metal or alloy parts where precise tolerances are required in the finished product. More particularly, the present invention relates to a parabolic antenna comprising a backing section and reflector made of deformable material, for instance metal or alloy, the backing section and reflector being mated to define a hollow interior cavity that is filled with a rigid support structure comprising a closed-cell foam. The present invention also particularly relates to a method of forming accurately dimensioned parts having close tolerances, such as transmission antennas, wherein a deformable material skin, for instance an antenna reflector of metal, is maintained in exact conformance with a vacuum buck, the vacuum buck having a configuration corresponding to the close tolerances of the preferred configuration of the completed part, and wherein a closed-cell foam slurry is provided, the cured foam forming a rigid support structure adequate to maintain the deformable material skin in the preferred configuration thereof following removal of the product from the vacuum buck.
Parabolic antennas generally have been around for a number of years and have, in the past several decades, become more and more widely used residentially and commercially for wireless television services, as well as other signal-communications applications. For instance, the advent of direct satellite television service, and the comparative xe2x80x9cminiaturizationxe2x80x9d of the receiving and transmitting antennas have driven, and promise to continue driving, consumer demand for these goods and services. Recent advances in communications technology in particular have led to the development of earth-bound antennas with diameters on the order of tens of centimeters, rather than tens of feet, that are capable of receiving and transmitting signals.
One important consideration in the manufacture and design of such antennas is the fact that, necessarily, antennas are employed in all variety of climates. While parabolic antennas are relatively simple in their design, the fact that signal reception and transmission is dependent upon the shape of the reflector face, or xe2x80x9cdishxe2x80x9d, renders their precise manufacture difficult and, sometimes, expensive. The importance of dish tolerances is especially pronounced in transmission antennas, where variations in the surface of the dish too far from a desired curvature will significantly degrade transmission performance.
Conventional antennas, for instance of the type used for residential satellite reception, are typically composed of a metal skin, manufactured, for example, by stamping. Antenna formed in this fashion do not, by reason of shape xe2x80x9cmemoryxe2x80x9d properties of the commonly used materials, retain their preferred curvatures. These drawbacks make such antennas prone to performance degradation, and render them particularly ill-suited to use as transmitting antennas.
In the past, one of the named inventors of this application developed an improved method for forming an antenna having sufficiently close tolerances in the reflector, the method comprising placing one of two panels for an antenna on a vacuum die, and connecting to both panels a structural means such as a plurality of undulating strips to interlock the panels. This methodology is more particularly described in U.S. Pat. No. 4,791,432, issued to Piper et al., the disclosure of which is incorporated herein by reference in its entirety. However, the method of this patent is complicated, requires considerable parts fabrication relative to the structural means, and so is not suited to the inexpensive mass-production of antenna.
Consequently, there is a need for a parabolic antenna that is simple but robust in construction, economical to manufacture, while at the same time able to retain a reflector curvature of high tolerances even through variations in ambient temperatures, wind loading, and other environmental influences.
The present invention addresses and solves the problems discussed above, and encompasses other features and advantages, by providing a parabolic, or dish-type, antenna comprising a backing section and a reflector of deformable material, such as polymer, metal, alloy, etc., the backing section and reflector being mated to define a hollow interior cavity that is filled with a rigid support structure comprising a closed-cell foam. Advantageously, the rigid support foam provides accurate shape retention for the preferred parabolic curvature of the antenna reflector, even through variations in temperature, wind loading, and other environmental influences.
The present invention also provides an economical and efficient method for forming accurately dimensioned parts having close tolerances, including parabolic antenna of the type of the inventive apparatus, the method comprising the steps of:
(a) providing a backing section and a reflector made of deformable material, the backing section and reflector being mateable to define a hollow interior cavity, and at least the reflector having a first curvature;
(b) providing a forming die including a male portion comprising a vacuum buck having a curved surface of predetermined tolerances exactly corresponding to a second, preferred curvature of the reflector, and a female portion dimensioned to receive the backing section therein;
(c) positioning and maintaining the reflector on the vacuum buck under vacuum pressure in conformance with the curved surface corresponding to the second, preferred curvature of the reflector;
(d) mating the backing section to the reflector;
(e) capturing the backing section and reflector in the mated condition thereof between the male and female portions of the forming die;
(f) injecting an expandable, closed-cell foam slurry into the hollow interior cavity defined between the mated backing section and reflector;
(g) while maintaining the reflector on the vacuum buck in conformance with the curved surface corresponding to the second, preferred curvature the curved surface corresponding to the second, preferred curvature of the reflector, curing the closed-cell foam slurry to form a rigid support structure; and
(h) releasing the vacuum pressure at the vacuum buck to thereby form an antenna wherein the reflector has a curvature corresponding to the second, preferred curvature.